Powertrain Controls - ECM/PCM

Diagnostic Chart:

EGR Electrical Circuit:

CIRCUIT DESCRIPTION
The Exhaust Gas Recirculation Solenoid Vacuum (EGR SV) valve is controlled by the Engine Control Module (ECM). System voltage is applied to the EGR SV valve from the Main relay. When the driver in the ECM closes, the EGR SV valve is activated.

Diagnostic Trouble Code (DTC) 51 will set if the following conditions are met:
^ System is operating in "closed loop" operation.
^ Difference of Manifold Absolute Pressure (MAP) sensor between EGR SV valve is On and when Off is less than a calibrated value.

DTC CHART TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. This will check EGR SV valve circuit for a short to ground.
2. Checks for voltage from the Main relay.
3. Checks the EGR SV valve circuit for short to ground or a faulty ECM.
4. Checks the EGR SV valve circuit for an open GRN wire.
5. Checks for proper resistance of the EGR SV valve.

DIAGNOSTIC AIDS
Closely check all vacuum hoses to the Throttle Body Fuel Injection (TBI) and the EGR valve. Also check the MAP sensor vacuum hose for leaks or restrictions. In "closed loop" operation with EGR enabled, the ECM will periodically turn "OFF" the EGR SV valve. If the corresponding manifold pressure change is less than a calibrated value, the ECM determines that a fault exists in the EGR system and sets a DTC 51.

For EGR system mechanical diagnosis, refer to Emission Control Systems / Exhaust Gas Recirculation / Testing and Inspection. Testing and Inspection

INTERMITTENT MALFUNCTIONS
An intermittent malfunction may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.